1. Field of the Invention
The present invention relates to an operating theater lamp comprising at least one discharge lamp which is arranged in a lamp body, is made in an approximately cylindrical shape and illuminates a site of an operation via optical means.
2. Description of the Related Art
The sufficient illumination of body cavities or operation channels generally represents a particular problem, since surgeons nowadays demand dimmable operating theater lamps having an illuminance in the region from approximately 60 to 130 klx. These high illuminances are necessary, on the one hand, since the light rays of the operating theater lamp are shaded by the head and the hands of the surgical personnel. On the other hand, for small and deep operation sites, high illuminances are required because the light rays have to be reflected downwardly at the wound edges to illuminate the surgical wound in depth. Approximately 90% of the incident light energy is absorbed by the red body tissue, i.e. only approximately 10% is reflected and reaches into the depth of the wound.
A dimmability of operating theater lamps, for example to a value of 60 klx, is necessary when the site of operation is only shallow or only extends slightly depth-wise. The same applies to the case when human skin is illuminated, which has a substantially higher degree of reflection than the red body tissue. Finally, dimmability is required when the operating theater lamp is set such that no shading, or only slight shading, takes place by the surgical personnel.
Usual operating theater lamps have previously been fitted with halogen lamps which can be controlled or regulated in their light emission by electronic dimmers. Here, the change in the light quality, in particular in the color rendition properties by the electrical dimming of the halogen lamps is low. It is, however, problematic that only approximately 8% of the electrical power is converted into light, i.e. more than 90% of the electrical power is converted into thermal energy, which puts stress on the surgical personnel since the lamp body is usually located in direct proximity to their heads. For this reason, operating theater lamps have already been developed with discharge lamps whose energy balance is much more favorable. However, these discharge lamps strongly change the light color with an electrical dimming. An electrical dimming is not possible ac all in some cases.